A cellular wireless network comprises multiple base stations, where each base station transmits to (downlink or DL) and receives from (uplink or UL) a plurality of mobile users in its coverage area. The explosion in data traffic in wireless cellular networks has created a need for rapid expansion of network capacity to cope with increasing user demand. Carrier aggregation provides one method to increase network capacity. With carrier aggregation, a base station simultaneously transmits data to, or receives data from, mobile user equipment (UE) on multiple carriers in the same or different RF bands. For example, in a cellular system complying with the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) standards, carrier aggregation has been standardized in LTE Releases 10 and 11 for both intra-band and inter-band operation. The cost of mobile UEs is strongly dependent upon the cost of the RF front end, including the mixers, oscillators and radio amplifier, which is designed to work in a specific RF band(s). To maximize return on investment, mobile UE vendors strive for equipment that can be used in both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes as well as in the most widely deployed RF bands across all geographic regions.
On the other hand, the cost of RF spectrum is a significant bottleneck in the deployment of ubiquitous and high data rate wireless communication systems. Cellular network operators acquire RF spectrum based on several factors including the size of allocated spectrum chunks (e.g., higher RF bands are better) and optimized coverage (e.g., lower frequency bands provide better in-building penetration). Furthermore, widespread adoption of a particular band guarantees that there would be mobile devices supporting that band. Based on these factors, a network operator may own spectrum in both FDD and TDD bands and may want to configure carrier aggregation for a UE on both TDD and FDD component carriers.